Canal and river invasive species

Not all the plants and animals living in our canals and rivers are native to the UK. Some species have been introduced, often with disastrous results for our precious ecosystems.

American Signal Crayfish coming out of water onto grass

Invasive species can have a devastating effect on native canal and river wildlife, as they compete against each other for food, space, sunlight and water. The animals can often be bigger and more aggressive, while the plants can choke canals and rivers with their rapid growth.

Learn more about the most common invasive species that pose a threat on our waterways.

American mink

Close up, American mink resemble something between a small cat and a ferret, and prey on water voles

Chinese mitten crab

These Asian crustaceans have a ravenous appetite for almost anything that gets in their way

Floating pennywork covering most of canal with boat moored at side

Floating pennywort

This highly invasive plant grows up to 20cm per day and is responsible for taking oxygen from native wildlife

Giant hogweed

This dark-green giant contains sap that can burn skin when exposed to sunshine

Himalayan balsam

This densely growing pink and red-stemmed weed stifles any native grasses and plants in its path

Japanese knotweed

Japanese knotweed crowds out native vegetation, erodes riverbanks and causes structural damage

Killer and demon shrimp

Both species and their eggs can easily be transported around in damp clothing and equipment, as they can survive for a long time out of water

New Zealand pigmyweed

The weed has forms a dense mat over the water's surface that blocks out light and oxygen

Signal crayfish

These 15cm-long beasts are aggressive, breed faster than native species, and damage banks with their burrowing

Terrapins

Britain's inland waterways were a safer place for bird eggs and insect larvae before these reptiles came along

Water fern

Water fern forms dense mats on the water’s surface and poses a hazard by appearing solid

Zebra mussel

These molluscs rapidly form large colonies that attach to almost any submerged hard surface, impeding the smooth running of canal gates and sluices

The battle with invasive species

Our teams of ecologists and volunteers work tirelessly to eradicate invasive species from our canals and rivers. Find out more about some of the techniques used to combat these problematic plants and animals.